Food packaging film

ABSTRACT

In the present invention, there is provided a food packaging film which is excellent in workability, processability, productivity, gas barrier properties, low-temperature heat sealing properties, safety and mechanical strengths, which can be used as an alternative film to generally used cellophane/wax films, and can be suitably used as a packaging film for melting cheese. The food packaging film according to the present invention comprises at least five layers of a heat seal layer/an adhesive layer/a gas barrier layer/an adhesive layer/a heat seal layer, which heat seal layer comprises an olefin-based resin and melts at not lower than 60° C. and lower than 90° C.

This application is a divisional of application Ser. No. 12/740,151filed Jul. 29, 2010, which in turn is the U.S. national phase ofInternational Application No. PCT/JP2007/001179, filed 29 Oct. 2007, theentire content of which is hereby incorporated by reference in thisapplication.

TECHNICAL FIELD

The present invention relates to a food packaging film. Morespecifically, the present invention relates to a food packaging filmwhich is excellent in workability, processability, productivity, gasbarrier properties, low-temperature heat sealing properties, safety andmechanical strengths, can be used as an alternative film to generallyused cellophane/wax films, and can be suitably used as a packaging filmfor melting cheese.

BACKGROUND ART

When producing processed cheese, a cellophane/wax film which is a sheetfilm and produced by coating the wax onto the surface of cellophane (forexample “Paraseal” (registered trademark) manufactured by NIKKANINDUSTRIES Co., Ltd.) is usually used, and first, a block of processedcheese packaged with the cellophane/wax film (about 1 to 10 kg weight)is produced. Concretely, the cellophane/wax film is folded to a box-likeshape and fixed to the inside of a stainless cheese forming case, aprescribed amount of melted cheese at 80 to 90° C. are fed thereinto,the cellophane/wax film is folded so as to remove air bubbles to packagethe cheese, a stainless case cover is set thereon, and the case isturned over. The inside and outside surfaces of film is fusion-sealed bythe wax which is melted by the heat and weight of cheese so that thecheese is air-tightly packaged (for example, refer to Patent Documents 1and 2). A block of cheese after refrigeration storage and solidified(block cheese) is taken out from the stainless case, the block cheese isprocessed to a desired shape, and finally, the cellophane/wax filmpackage is removed therefrom.

Although the above cellophane/wax film has an advantage that the sealingcan be made by the heat and weight of cheese, there are problems that(1) the cellophane/wax film is poor in the mechanical strength so thatit is easy to break and foreign matters are got inside thereof; (2) whenthe melted wax is leaked out from the cellophane/wax film and adhered tothe shaping case, it is difficult to take out the block cheese from theshaping case to deteriorate the workability; (3) although the melted waxis not harmful, there is a possibility to remain the wax on the surfaceof cheese and it is not preferable; and (4) by the relationship betweenthe used cellophane and wax, blue-color printing is impossible so thatit is difficult to find any scratches (usually, in food packaging,blue-colored packaging materials are used for preventing any foreignmatters from getting inside.

As replacements of cellophane/wax film, there has been proposed a filmusing a plastic film instead of cellophane so as to enhance themechanical strengths (for example, refer to Patent Document 2). However,since this still uses wax for air-tightening, the above problems (2) and(3) are still not overcome.

Further, there has been proposed a process for air-tightening by using afilm having heat seal property and heat sealing thereof (for example,refer to Patent Document (3) and this process is used forindividually-packaging of sliced cheese. However, in this process, anyextra film portion is necessary to provide heat sealed portions, andwhen the heat sealing thereof is not conducted under deaeration, air isremained between the cheese and film so that this leads to gettingmoldy. Also, this operation under deaeration is a major hurdle in theworkability. Further, in this process, since any extra film portion suchas heat sealed portions is required, there is a possibility that tracesand wrinkles caused by the extra film portion are formed on the surfaceof cheese so that loss of cheese content and deterioration of productvalue are caused. Therefore, it is difficult to apply this process topackaging of cheese block.

Further, there is unknown a packaging film for block cheese capable ofair-tight packaging by fusion-sealing method of envelope formationshape.

-   Patent document 1: Japanese Utility Model Application Laid-Open    (KOKAI) No. 5-35786-   Patent document 2: Japanese Patent Application Laid-Open (KOKAI) No.    6-40485-   Patent document 3: Japanese Patent Application Laid-Open (KOKAI) No.    10-750

DISCLOSURE OF THE INVENTION Problem to be Solved by the Invention

The present invention has been made so as to overcome the aboveproblems, an object of the present invention is to provide a foodpackaging film which can be heat-sealed by heat of fed melted foodhaving a temperature of not lower than 60° C. and lower than 90° C. suchas melted cheese without other heat-sealing operation, which can be usedas an alternative film to generally used cellophane/wax films, and canbe suitably used as a packaging film for melting cheese, and which isexcellent in workability, processability, productivity, gas barrierproperties, low-temperature heat sealing properties, safety andmechanical strengths. Especially, an object of the present invention isto provide a food packaging film capable of solving a problem of poormechanical strengths which is a problem of conventional plastic filmsfor packaging block cheese (a part of broken piece of film is remainedon the surface when removing the film), a problem of delamination ofadhesive layer (by heat or oil of content), and a problem that in caseof using a colored resin added into the heat seal layer instead ofprinting so as to preventing from remaining broken film pieces, thecoloring pigment is transferred and attached to the content by heat ofcontent, as well as capable of remarkably reducing the cost to beincreased by coating step and printing step.

Means for Solving the Problem

As a result of present inventors' earnest study to solve the aboveproblems, it has been found that by a film comprising at least fivelayers of a heat seal layer/an adhesive layer/a gas barrier layer/anadhesive layer/a heat seal layer, which heat seal layer comprises aspecific resin, the above problems can be solved. Thus, the presentinvention has been attained on the basis of the above finding.

In an aspect of the present invention, there is provided a foodpackaging film comprising at least five layers of a heat seal layer/anadhesive layer/a gas barrier layer/an adhesive layer/a heat seal layer,which heat seal layer comprises an olefin-based resin and melts at notlower than 60° C. and lower than 90° C.

Effect of the Invention

Since the food packaging film according to the present invention isexcellent in workability, processability, productivity, gas barrierproperties, low-temperature heat sealing properties, safety andmechanical strengths, it can be used as an alternative film to generallyused cellophane/wax films, and can be suitably used as a packaging filmfor foods such as melting cheese.

PREFERRED EMBODIMENT FOR CARRYING OUT THE INVENTION

The present invention is described in more detail below. The foodpackaging film according to the present invention comprises at leastfive layers of a heat seal layer/an adhesive layer/a gas barrierlayer/an adhesive layer/a heat seal layer. By having the above fivelayers structure in the film, various folding shapes and air-tightsealing form can be practiced regardless of which sides of film areselected because the heat seal layers are provided at the both surfacesof film. At least other optional layer may be inserted between the aboveoptional contacting layers, respectively.

As the above gas barrier layer, there is no limitation as long as thelayer has gas barrier property. As the resin constituting the gasbarrier layer, there are exemplified polyamides (PA), ethylene-vinylalcohol copolymer (EVOH), polyethylene terephthalate (PET), polyethylenenaphthalate (PEN), polycarbonates (PC), or the like. Of these,polyamides (PA) and ethylene-vinyl alcohol copolymer (EVOH) arepreferred, especially polyamides (PA, nylons) are preferred. As thepolyamide, there are exemplified nylons 4, 6, 7, 8, 11, 12, 6·6, 6·10,6·11, 6·12, 6T, 6/6·6, 6/12, 6/6T, 6I/6T, MXD6, or the like.

When fill the melting cheese into the box-shaped film, the film maybecome not elastic by softening due to steam generated from the meltingcheese (for example 50° C.) so that the film folds undesirably and thefilling the cheese may be troubled. Therefore, it is preferred to use amaterial which is not affected by the steam generated from the fillingfood. Further, after filling the melting cheese and the film is heatedthereby at not lower than 60° C., if the film is sufficiently softened,it is difficult to form fold lines and the film become a tunnel-likeshape structure. Namely, it is required for the film that during fillingthe melting cheese, the film need to be elastic so as not to foldthereby, when folding and packaging the melting cheese, the film need tobe softened so as to completely fusion-seal it. In view of the above, ofthese polyamides, MXD6 is especially preferred because ofheat-resistance rigidity temperature is suitable to the above range.

The thickness of gas barrier is usually 2 to 50 μm, preferably 4 to 30μm. When the thickness of gas barrier is less than 2 μm, the film is notelastic, in case of used for cheese packaging, the film may be foldedduring feeding melting cheese so that the melting cheese may not befilled. When the thickness of gas barrier is more than 50 μm, althoughthe film is elastic, the heat from the melting cheese may not betransferred when heat-sealing by folding the film present in upper sideof cheese so that the heat sealing may not be completed. It is preferredthat the gas barrier layer comprises not less than 70% by weight ofresin having a density of not less than 0.9150. In this embodiment, itcan be prevented that low molecular compounds such as a pigment and/ordye used in coloring the gas barrier layer exude onto the film.

In the food packaging film according to the present invention, theadhesive layer is required so as to adhere the above gas barrier layerand heat seal layer. The adhesive layer preferably comprises adhesiveresin layer comprising a modified polyolefin resin. The modifiedpolyolefin resin is produced by copolymerizing or graft polymerizingα,β-unsaturated carboxylic acid or derivatives thereof to a polyolefinresin which comprises ethylene and/or propylene as the mainly component.

As the above polyolefin resin, there are exemplified polyethylene,polypropylene, ethylene-propylene copolymer, ethylene-butene-1copolymer, ethylene-vinylacetate copolymer, ethylene-acrylic acidcopolymer, ethylene-ethylacrylic acid copolymer, ethylene-sodiumacrylate copolymer, or the like.

As the above copolymerized α,β-unsaturated carboxylic acid orderivatives thereof, there are exemplified acrylic acid, methacrylicacid, sodium acrylate, zinc acrylate, vinylacetate,glycidylmethacrylate, or the like. These are contained in the molecularchain in a range of not more than 40 mol %. As examples of copolymerizedmodified polyolefin resin, ethylene-vinylacetate copolymer,ethylene-acrylic acid copolymer, ethylene-ethylacrylic acid copolymer,ethylene-sodium acrylate copolymer,

As the above grafted α,β-unsaturated carboxylic acid or derivativesthereof, there are exemplified acrylic acid, methacrylic acid,ethacrylic acid, maleic acid, fumaric acid, anhydrides thereof andesters thereof. Of these modifying compounds, maleic anhydride isespecially preferred. Further, the graft percentage is selected from arange of 0.01 to 25% by weight, preferably 0.05 to 1.5% by weight.

The graft polymerization is conducted by an ordinary method. Usually, itis conducted by melt-mixing a polyolefin resin and α,β-unsaturatedcarboxylic acid or derivatives thereof at a resin temperature of 150 to300° C. In the graft polymerization, in order to conduct the reactioneffectively, an organic peroxide such asα,α′-bis-t-butylperoxy-p-diisopropylbenzene is blended thereinto at anamount of 0.001 to 0.05% by weight.

The thickness of adhesive layer is usually not less than 2 μm,preferably 3 to 20 μm. When the thickness of adhesive layer is less than2 μm, the adhesive property between the gas barrier layer and adhesivelayer is poor so that there is a possibility that the heat seal layer isreleased from the gas barrier layer when the heat seal layer is fused bythe heat of melted cheese. When the adhesive layer is too thick, theproduction cost is increased while the adhesive property is no longerimproved more. Further, it is preferred that 70% by weight or more ofthe resin constituting the adhesive layer comprises a resin having adensity of not less than 0.9150 g/cm³. In this embodiment, it can beprevented that low molecular compounds such as a pigment and/or dye usedin coloring the gas barrier layer exude onto the film surface throughthe adhesive layer.

The heat seal layer comprises an olefin-based resin whose constitutingmaterial is not limited as long as it can be fused at not lower than 60°C. and lower than 90° C., preferably 60 to 80° C., more preferably 60 to70° C. and can be used for food packaging. As the above material, thereare exemplified low density polyethylene (hereinafter may be abbreviatedas “LDPE”), polypropylene (PP) and polyethylene obtained bypolymerization in the presence of a metallocene catalyst (hereinaftermay be abbreviated as “M-LLDPE”). Further, in case where a materialhaving a melting point higher than the above defined range as it is, themelting point may be adjusted to the above defined range by blending theother resin thereinto to depress the melting point.

The heat seal layer is fusion-sealed by the heat of food and acts toair-tightly package the food. In addition, in case where any layer otherthan the heat seal layer is colored, the heat seal layer acts to preventfrom migrating the coloring agent to the food surface by the heat offood. Namely, by the presence of heat seal layer, it is possible to usea colored film as the gas barrier layer so that the printing step on thefilm surface so as to find any film breaking is not required and then,it is possible to reduce the post-processing and cost significantly.

In the above materials, M-LLDPE is preferred because it is less stickydue to less content of low molecular weight components and smell-less.It is more preferred that the heat seal layer comprises 40 to 95% byweight of M-LLDPE. M-LLDPE is a linear low-density polyethylene resin,namely copolymer of ethylene with α-olefin having carbon number of 3 to13 (ethylene content: 86 to 99.5 mol %), which M-LLDPE is obtained bygas-phase process, liquid-phase process or solution process in thepresence of metallocene catalyst (single-site catalyst). As concreteexamples of α-olefin, there are mentioned propylene, butene-1,hexene-1,4-methylpentene-1, octene-1, decene-1 and dodecene-1. The meltindex (MI) of M-LLDPE is usually 0.1 to 20 g/10 min (230° C.). M-LLDPEhas a ratio (Mw/Mn) of weight average molecular weigh (Mw) to numberaverage molecular weight (Mn) is usually 1.5 to 4.0, preferably 2 to 3.5and a polymer having a sharp molecular weight distribution and sharpcomposition distribution is preferred.

The melting point of M-LLDPE is usually 60 to 70° C., preferably 60 to65° C. When the melting point of M-LLDPE is lower than 60° C., there isa possibility that the film is fusion-sealed during storage thereof insummer. When the melting point of M-LLDPE is higher than 70° C., it maybe difficult to fusion-seal thereof at 70 to 90° C. As described above,since M-LLDPE is a homogeneous polymer having the sharp molecular weightdistribution and sharp composition distribution and has the less contentof low molecular weight components, M-LLDPE has such a property of rapidfusion-sealing at the fusion-sealing temperature of the film accordingto the present invention.

The density of M-LLDPE is usually not less than 0.805 g/cm³ and lessthan 0.905 g/cm³, preferably 0.805 to 0.880 g/cm³. When the density ofM-LLDPE is not less than 0.905 g/cm³, it may be difficult to fusion-sealat the temperature of 70 to 90° C. Although the density of M-LLDPE ofless than 0.805 g/cm³ is possible, such product may be difficult toavailability.

The melt flow rate (MFR) of M-LLDPE is usually 0.5 to 15.0 g/10 min,preferably 0.8 to 5.0 g/10 min. When the MFR is less than 0.5 g/10 min,the extruder tends to be overloaded and the resin tends to be heated sothat fish eye and gelation tend to occur. When the MFR is more than 15.0g/10 min, it may be difficult to feed the resin into a mold uniformly sothat such a problem that the resin is not partially extruded may arise.As the commercial product of M-LDDPE, there is exemplified “Carnel”(trade name) manufactured by Japan Polyethylene Corporation.

As described above, LDPE and PP can be used for the heat seal layer. Incase of using LDPE and PP having a melting point of 90° C. or higher,the melting point can be adjusted within the above defined range byblending the other resin or blending the same kind resin having lowermelting point (for example, M-LLDPE) so as to depress the melting point.Especially, it is preferred that the heat seal layer comprises 40 to 75%by weight of M-LLDPE having a density of less than 0.905 g/cm³ and 25 to60% by weight of LDPE having a density of not less than 0.905 g/cm³,preferably not less than 0.915 g/cm³.

In the above embodiment (1), as the low-density polyethylene having thedensity of not less than 0.905 g/cm³, there are exemplified low densitypolyethylene (hereinafter may be abbreviated as “LDPE”) and/or linearlow-density polyethylene (hereinafter may be abbreviated as “LLDPE”).LLDPE is a copolymer which comprises ethylene as the mainly componentand α-olefin, which has a density of 0.905 to 0.945 g/cm³, and which isproduced by various polymerization processes such as gas-phase process,solution process and suspension polymerization process using variouscatalysts such as Ziegler catalyst, chromium-based catalyst andmetallocene catalyst under low/medium pressure or high pressure. As theabove α-olefin, there are exemplified propylene, butene-1, hexene-1,octene-1,4-methylpentene-1, 4-methylhexene-1,4,4-dimethylpentene-1,nonene-1, decene-1, undecene-1 and dodecene-1.

The melt index rate of the above LDPE and LLDPE according to JIS K721 at190° C. under load of 2.16 kgf is usually 0.05 to 50 g/10 min,preferably 0.1 to 20 g/10 min.

Incidentally, as the concrete examples of the above, LLDPE (commercialproducts), Unipole (by Union Carbide, Corporation), Dowlex (by DowChemical Company), Screar (by DuPont Canada), Marlex (by Philips),Neozex and Ultzex (by Mitsui Chemicals, Inc.), Nisseki Linirex (byNippon Oil Corporation) and Stamirex (by DSM) are mentioned.

Further, by adding an anti-blocking agent and lubricant into the resinssuch as M-LLDPE, LDPE and PP, the film producibility can be enhancedwhile maintaining the melting point thereof within the defined range.The amount of anti-blocking agent and lubricant added is usually 5 to40% by weight, preferably 10 to 30% by weight. When the adding amount ofanti-blocking agent and lubricant is more than 40% by weight, thestrength of film may be poor, it may be difficult to fusion-seal and theanti-blocking agent and lubricant tend to drop on the cheese surfacefrom the film so that it is not preferable. When the adding amount ofanti-blocking agent and lubricant is less than 5% by weight, blocking offilm tends to occur.

The anti-blocking agent and lubricant are not limited as long as havinghigh safety in order to use for a food packaging film, and known organicfine particles and/or inorganic fine particles can be used. As theanti-blocking agent comprising organic fine particles, there areexemplified fine particles comprising homopolymer or copolymer ofpolystyrene, polyethylene, polyamides, polyesters, polyacrylates,polymethacrylates, epoxy resins, polyvinyl acetate and polyvinylchloride, which may have any crosslinking agent. On the other hand, asthe anti-blocking agent comprising inorganic fine particles, there areexemplified talc, kaolin, silica, calcium carbonate and glass powder.The average particle size of the above anti-blocking agent is usually 1to 10 μm. Further, the inorganic fine particles may be used in acomposition form where they are previously blended to the resin (masterbatch).

The thickness of heat seal layer is usually 5 to 50 μm, preferably 5 to30 μm. When the thickness of heat seal layer is less than 5 μm, theremay be a possibility of insufficient heat sealing strength at the heatsealing portion. There is no problem when the thickness of heat seallayer is more than 50 μm, however, the thickness is too thick beyondnecessity, it is a waste of material and costly.

The thickness of food packaging film according to the present inventionis usually 40 to 120 μm, preferably 60 to 100 μm. When the filmthickness is less than 40 μm, the film is not elastic, in case of usedfor cheese packaging, the film may be folded during feeding meltingcheese so that the melting cheese may not be filled. When the filmthickness is more than 120 μm, although the film is elastic, the heatfrom the melting cheese may not be transferred when heat-sealing byfolding the film present in upper side of cheese so that the heatsealing may not be completed.

Next, the process for producing the feed packaging film according to thepresent invention is explained. The feed packaging film according to thepresent invention is preferably produced by coextrusion inflation methodto obtain a cylindrical shape laminate film. As the inflation method,there may be employed a known method (water-cooling method) comprisingdrawing a film formed by extrusion from a cyclic dye to downward of dye,cooling thereof by blowing cooling air to the film, thereafter furtherquenching thereof with water and winding thereof. Usually, such methodcomprises using an equipment comprising an airing equipment to blowcooling air to the film placed at downward of cyclic dye, and guideplates and a winding roll placed at downward of the airing equipmentsequentially; coextruding plural kinds of material resins from thecyclic dye so as not to stretch the film substantially; cooling the filmby passing through the airing equipment; quenching the film with water;feeding the quenched cylindrical shape film to the winding roll throughthe guide plates to fold thereof; and winding thereof as a laminatefilm.

The food packaging film according to the present invention canair-tightly heat seal by the heat of fed melting food. Namely, a foodmelted at 80 to 90° C. is fed into the food packaging film according tothe present invention whose shape is adjusted to box-like shape and thefilm is closed so that the film surfaces are fusion-sealed by the heatof food and the film packages the food air-tightly. The food packagingfilm according to the present invention can be preferably used forpackaging a food which is melting state (liquid) at 80 to 90° C. whenpackaging and is solid at ordinary temperature such as another ofcheese, chocolate, pudding, jam, marmalade, jelly, and agar-agar.Further, the food packaging film can be used for air-tightly packaging aprocessed food. For example, a processes food heated at 80 to 90° C. isfed into the food packaging film according to the present inventionwhose shape is adjusted to box-like shape and the film is closed so thatthe film surfaces are fusion-sealed by the heat of food and the filmpackages the food air-tightly. As the processed foods, there areexemplified in addition to liquid foods including solids such as stew,curries, and miso soups and prepared meats such as steak, hamburgersteak, sausages, and hams, Chinese daily dishes, the Japanese food dailydishes, the European food daily dishes, rice, rice gruels, and ricecakes, etc. Further, the film according to the present invention ispreferably used for air-tight packaging of beverage goods as long asprocessed by the heating sterilization and the extraction at thetemperature of 80 to 90° C., such as water, natural water, ion water,health drink, various healthy drinks, various soups, various juices,milks, green tea, teas, coffees, cocoas, and other various soft drinks.Therefore, these embodiments are also within the scope of the presentinvention.

EXAMPLES

The present invention is described in more detail below by way of theexamples. However, the examples are only illustrative and therefore thepresent invention is not limited to these examples. In the followingExamples and Comparative Examples, all “parts” and “percents (%)” are byweight unless otherwise noted. The materials used in each Example andComparative Example are shown in the following.

Resin for the Gas Barrier Layer:

(A-1) 6 Nylon (“NOVAMID 1010” manufactured by MitsubishiEngineering-Plastics Corporation).

Resin for the Adhesive Layer:

(B-1) Adhesive polyethylene (“Modic-AP M552” manufactured by MitsubishiChemical Corporation).

Resin for the Heat Seal Layer:

(C-1) polyethylene (M-LLDPE, density: 0.880 g/m³, Mw/Mn=2.3, “Carnel”manufactured by Japan Polyethylene Corporation).

(C-2) Crystalline olefin-ethylene/butylene-crystalline olefin blockcopolymer (CBEC, density: 0.880 g/m³, “DYNARON 6200P” manufactured byJSR corporation).

(C-3) Ethylene-α-olefin copolymer (density: 0.870 g/m³, “TAFMER P0480”manufactured by Mitsui Chemicals, Inc.).

(C-4) Low-density polyethylene (LDPE, density: 0.918 g/m³, “NOVATEC LDLF240” manufactured by Japan Polyethylene Corporation).

(C-5) Polypropylene (density: 0.900 g/m³, “NOVATEC PP FG3D” manufacturedby Japan Polypropylene Corporation).

(C-6) Anti-blocking agent (average particle size: 3 μm, 8% zeolitemasterbatch “LX-ABI” manufactured by Japan Polyethylene Corporation).

(C-7) Anti-blocking agent (2% erucamide masterbatch “NOVATEC PE-AF”manufactured by Japan Polyethylene Corporation).

The evaluations of food packaging film were conducted by the followingmethods.

(1) Evaluation of Heat Sealing:

After heat sealing of five layers laminated film obtained in eachExample and Comparative Example at the temperature of 55 to 75° C.,under pressure of 1.45 kg/cm³ for 30 seconds, the seal strength thereofwas measured according to the method of JIS A 1707. When the sealstrength is not less than 3N/15 mm width, the heat sealing is completed.

Examples 1 to 12

The above (A-1) as the resin for gas barrier layer, the above (B-1) asresin for the adhesive layer and the resins shown in Tables 1 and 2 asresin (anti-blocking agent) as the heat sealing layer were usedrespectively, and using a five kinds five layers inflation moldingmachine (die diameter: 250 mmφ), die lip: 2 mm and die temperature: 240°C.), a five layer tubular laminate film comprising heat seal layer(outside)/adhesive layer/gas barrier layer/adhesive layer/heat seallayer (inside) was produced. As the thicknesses of heat seal layers, thethickness of outside seal layer was 20 μm and the thickness of insideseal layer was 28 μm, the thickness of each adhesive layer was 4 mm, thethickness of gas barrier layer was 24 μm, the total thickness of filmwas 80 μm and folding diameter was 350 mm. To the obtained foodpackaging film, heat sealing properties at various temperatures wereevaluated. The results are shown in Tables 1 and 2.

TABLE 1 Composition of heat seal Examples layer (% by weight) 1 2 3 4 56 M-LLDPE C-1 95 75 70 65 60 40 CBEC C-2 — — — — — — Ethylene-α-olefinC-3 — — — — — — copolymer LDPE C-4  5 25 30 35 40 60 PP C-5 — — — — — —Anti-blocking agent C-6 10 10 10 10 10 10 C-7  2  2  2  2  2  2 Heatsealing 55° C. X X X X X X evaluation at 60° C. ◯ ◯ X X X X respectiveheat seal 65° C. ◯ ◯ ◯ ◯ X X temperatures 70° C. ◯ ◯ ◯ ◯ X X 75° C. ◯ ◯◯ ◯ ◯ X 80° C. ◯ ◯ ◯ ◯ ◯ ◯ ◯: Heat sealed X: Non-heat sealed

TABLE 2 Composition of heat seal Examples layer (% by weight) 7 8 9 1011 12 M-LLDPE C-1 85 80 85 80 80 80 CBEC C-2 — — 15 20 — —Ethylene-α-olefin C-3 — — — — 15 20 copolymer LDPE C-4 — — — — — — PPC-5 15 20 — — — — Anti-blocking agent C-6 10 10 10 10 10 10 C-7  2  2  2 2  2  2 Heat sealing 55° C. X X X X X X evaluation at 60° C. X X X X XX respective heat seal 65° C. ◯ X ◯ X X X temperatures 70° C. ◯ ◯ ◯ ◯ ◯◯ 75° C. ◯ ◯ ◯ ◯ ◯ ◯ 80° C. ◯ ◯ ◯ ◯ ◯ ◯ ◯: Heat sealed X: Non-heatsealed

1.-10. (canceled)
 11. A method of making an air-tight food packagingcomprising: (a) forming a container of the food packaging filmcomprising at least five layers of a heat seal layer/an adhesive layer/agas barrier layer/an adhesive layer/a heat seal layer, which heat seallayer comprises an olefin-based resin and melts at not lower than 60° C.and lower than 90° C., in which the heat seal layer comprises 40 to 100%by weight of polyethylene obtained by polymerization in the presence ofa metallocene catalyst, or the heat seal layer comprises 40 to 95% byweight of the olefin-based resin and 5 to 40% by weight of ananti-blocking agent and/or a lubricant, (b) feeding a melted food havinga temperature of not lower than 60° C. and less than 90° C. into thecontainer, (c) folding the food packaging film, and (d) heat-sealing atleast part of a surface of one side and the surface of an opposite sideof the folded and overlapped food packaging film by heat of the fedmelted food having a temperature of not lower than 60° C. and less than90° C.
 12. The method according to claim 11, wherein the heat seal layerof the food packaging film comprises 40 to 75% by weight of polyethylenehaving a density of less than 0.905 g/cm³ and obtained by polymerizationin the presence of a metallocene catalyst, and 25 to 60% by weight oflow-density polyethylene having a density of not less than 0.905 g/cm³.13. The method according to claim 11, wherein the polyethylene of thefood packaging film is obtained by polymerization in the presence of ametallocene catalyst has a melting point of 60 to 70° C.
 14. The methodaccording to claim 11, wherein the gas barrier layer of the foodpackaging film comprises at least one polymer selected from the groupconsisting of polyamide, ethylene-vinylalcohol copolymer, polyethyleneterephthalate, polyethylene naphthalate and polycarbonate.
 15. Themethod according to claim 11, wherein the adhesive layer of the foodpackaging film comprises an unsaturated carboxylic acid-modifiedpolyolefin.
 16. The method according to claim 11, wherein the food ismelted cheese.
 17. The method according to claim 11, wherein the foodpackaging film is colored.
 18. A method of packaging a productcomprising the steps of: (a) forming a container for a food product froma food packaging film comprising at least five layers of a heat seallayer/an adhesive layer/a gas barrier layer/an adhesive layer/a heatseal layer, which heat seal layer comprises an olefin-based resin andmelts at not lower than 60° C. and lower than 90° C., in which the heatseal layer comprises 40 to 100% by weight of polyethylene obtained bypolymerization in the presence of a metallocene catalyst, or the heatseal layer comprises 40 to 95% by weight of the olefin-based resin and 5to 40% by weight of an anti-blocking agent and/or a lubricant, (b)filing the container formed in step (a) with a food product having atemperature of not lower than 60° C. and lower than 90° C., therebycausing the heat seal layer or layers in contact with each other tofusion seal from the heat of the food product thereby heat sealing thefood product in an air-tight container.